Brake system having drag reduction function and method of controlling the same

ABSTRACT

A brake system may have a drag reduction function of effectively attenuating drag by controlling the position of a pressurizing piston in a pressurizing cylinder through a motor to supply a fluid in a hydraulic line to the reserve tank such that negative pressure is created to forcibly withdraw the piston in a caliper, and a method of controlling the same. The brake system may include a pressurizing cylinder connected to a reserve tank to store a fluid, a motor to move a pressurizing piston forward, and a braking control unit to receive state information about the vehicle to determine whether the vehicle is braking or traveling, execute, when the vehicle is traveling, a negative pressure creation mode of driving the motor to move the pressurizing piston forward to create a negative pressure, and execute, when creation of the negative pressure is completed, a negative pressure maintaining mode.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit of Korean Patent Application No.10-2013-0165845, filed on Dec. 27, 2013 in the Korean IntellectualProperty Office, the disclosure of which is incorporated in its entiretyherein by reference.

BACKGROUND

1. Field

Embodiments of the present invention relate to a brake system having adrag reduction function and a method of controlling the same and, moreparticularly, to a brake system having a drag reduction function ofeffectively attenuating a drag phenomenon by controlling the position ofa pressurizing piston in a pressurizing cylinder connected to a reservetank through a motor to supply a fluid in a hydraulic line to thereserve tank such that negative pressure is created to force the pistonin a caliper to be withdrawn, and a method of controlling the same.

2. Description of the Related Art

Generally, a vehicle is provided with a brake system to selectivelydecelerate or stop the vehicle when necessary during traveling. Suchbrake system usually performs the braking operation by converting thekinetic energy of the traveling vehicle into thermal energy usingfriction and dissipating the produced heat into the ambient air.

That is, such brake systems are generally classified into a drum brakesystem and a disc brake system. In the case of the disc brake system,braking force is obtained from frictional force generated when acaliper, which is driven by hydraulic pressure generated in a mastercylinder according to manipulation of a brake pedal, applies pressure tobrake pads on both sides of a brake disc.

The aforementioned brake systems prevent production of a lost travelsection of a stroke by sensing that the driver presses the brake pedaland sending the pressure accumulated in an accumulator to wheelcylinders. With this method, however, if the hydraulic pressure by thedriver's foot force becomes greater than the pressure accumulated in theaccumulator, the accumulator may fail to send the accumulated pressureto the wheel, and rather the pressure produced by the driver's footforce may be accumulated, resulting in increase of the lost travelsection of the stroke. If the pressure of the accumulator issignificantly high, the pressure may be fully delivered when the driverdepresses the brake pedal. This may significantly contribute todegradation of brake feel.

In addition, a conventional brake system as disclosed in Korean PatentApplication Publication No. 2011-0125286 produces braking force throughfriction between the disc and the brake pads. This frictional force isproduced by the brake pads pushed by the hydraulic pressure createdthrough the driver's manipulation of the brake pedal. When braking isterminated, the frictional force is removed by separating the brake padsfrom the disc using the knock-back phenomenon occurring between thebrake pads and resilience (roll-back phenomenon) of a piston seal of thedisc caliper.

However, with this method, a drag phenomenon, which refers to incompleteseparation of the brake pads from the disc, may frequently occur. Inaddition, service life of the brake pads may be reduced and output maybe degraded due to unnecessary friction.

Accordingly, a brake system that is capable of completely separating thedisc and the brake pads to reduce drag is needed.

CITED REFERENCE Patent Document

Korean Patent Application Publication No. 2011-0125286 (Nov. 21, 2011),“Disc Brake”.

SUMMARY

Therefore, it is an aspect of the present invention to provide a brakesystem having a drag reduction function of effectively attenuating dragby controlling the position of a pressurizing piston in a pressurizingcylinder connected to a reserve tank through a motor to supply a fluidin a hydraulic line to the reserve tank such that negative pressure iscreated to force the piston in a caliper to be withdrawn, and a methodof controlling the same.

Additional aspects of the invention will be set forth in part in thedescription which follows and, in part, will be obvious from thedescription, or may be learned by practice of the invention.

In accordance with one aspect of the present invention, a brake systemto perform braking to decelerate or stop a vehicle includes apressurizing cylinder connected to a reserve tank adapted to store afluid, a motor to move a pressurizing piston forward in the pressurizingcylinder, and a braking control unit to receive state information aboutthe vehicle to determine whether the vehicle is braking or traveling,execute, when the vehicle is traveling, a negative pressure creationmode of driving the motor to move the pressurizing piston forward tocreate a negative pressure, and execute, when creation of the negativepressure is completed, a negative pressure maintaining mode ofmaintaining the negative pressure.

In the negative pressure creation mode, a Normally-Open valve of eachwheel may be closed, and the motor may be driven to move thepressurizing piston forward such that a fluid in a hydraulic line issupplied to the reserve tank.

In the negative pressure maintaining mode, a Normally-Open valve of eachwheel may be re-opened, a valve connecting the wheel to the pressurizingcylinder may be opened, a valve connecting the reserve tank to a wheelcylinder may be closed, a valve connecting the reserve tank to thepressurizing cylinder may be closed, and the pressurizing piston may bewithdrawn in the pressurizing cylinder until the pressurizing pistonreaches a flow passage connecting the reserve tank to the pressurizingcylinder, such that the negative pressure is maintained.

The state information about the vehicle may include information itemsmeasured respectively by a wheel speed sensor, a pressure sensor, anaccelerator pedal position sensor and a brake pedal position sensor,wherein the braking control unit may determine whether the vehicle isbraking based on brake pedal manipulation information and pedal pressureinformation of the state information about the vehicle, and determinewhether the vehicle is traveling based on accelerator pedal informationand wheel speed information of the state information about the vehicle.

The braking control unit may determine whether the creation of thenegative pressure has been completed after executing the negativepressure creation mode, and perform, when the creation of the negativepressure has not been completed, or execution of the negative pressuremaintaining mode is interrupted, offset calibration of calibrating aposition of the pressurizing piston.

The braking control unit may perform, when the execution of the negativepressure creation mode is interrupted or the creation of the negativepressure has not been completed, offset calibration of setting theposition of the pressurizing piston to an origin, and perform, when theexecution of the negative pressure maintaining mode is interrupted,offset calibration of setting a last position of the pressurizing pistonat an atmospheric pressure to an origin.

In accordance with another aspect of the present invention, a method ofcontrolling a brake system including a pressurizing cylinder connectedto a reserve tank adapted to store a fluid and a motor to move apressurizing piston forward in the pressurizing cylinder includesreceiving state information about a vehicle, determining whether thevehicle is braking or traveling based on the received state information,executing, when it is determined, in the determining, that the vehicleis traveling, a negative pressure creation mode of driving the motor tomove the pressurizing piston forward to create a negative pressure, andexecuting, when creation of the negative pressure is completed, anegative pressure maintaining mode of maintaining the negative pressure.

The executing of the negative pressure creation mode may include closinga Normally-Open valve of each wheel, and driving the motor to move thepressurizing piston forward such that a fluid in a hydraulic line issupplied to the reserve tank.

The executing of the negative pressure maintaining mode may includere-opening a Normally-Open valve of each wheel, opening a valveconnecting the wheel to the pressurizing cylinder, closing a valveconnecting the reserve tank to a wheel cylinder, closing a valveconnecting the reserve tank to the pressurizing cylinder, andwithdrawing the pressurizing piston in the pressurizing cylinder untilthe pressurizing piston reaches a flow passage connecting the reservetank to the pressurizing cylinder, such that the negative pressure ismaintained.

The executing may include determining, after executing the negativepressure creation mode, whether the creation of the negative pressurehas been completed, and performing, when it is determined in thedetermining that the creation of the negative pressure has not beencompleted, offset calibration of calibrating a position of thepressurizing piston.

The performing of the offset calibration may include performing, theexecution of the negative pressure creation mode is interrupted, offsetcalibration of setting the position of the pressurizing piston to anorigin, and performing, when the execution of the negative pressuremaintaining mode is interrupted, offset calibration of setting a lastposition of the pressurizing piston at an atmospheric pressure to anorigin.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects of the invention will become apparent andmore readily appreciated from the following description of theembodiments, taken in conjunction with the accompanying drawings ofwhich:

FIG. 1 is a block diagram illustrating a brake system having a dragreduction function according to an exemplary embodiment of the presentinvention;

FIG. 2 is a block diagram illustrating a braking control unit shown inFIG. 1;

FIG. 3 is a flowchart illustrating a method of controlling a brakesystem having a drag reduction function according to one embodiment ofthe present invention;

FIG. 4 is a diagram illustrating operation in a negative pressurecreation mode; and

FIG. 5 is a diagram illustrating operation in a negative pressuremaintaining mode.

DETAILED DESCRIPTION

Reference will now be made in detail to the embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings, wherein like reference numerals refer to like elementsthroughout.

FIG. 1 is a block diagram illustrating a brake system having a dragreduction function according to an exemplary embodiment of the presentinvention, and FIG. 2 is a block diagram illustrating a braking controlunit shown in FIG. 1.

Referring to FIG. 1, the brake system having a drag reduction functionaccording to this embodiment includes a braking control unit 50. Thebraking control unit 50 receives state information about a vehicle anduses the received state information to perform, when the vehicle istraveling, a negative pressure creation mode of driving a motor to movea pressurizing piston in a pressurizing cylinder to supply a fluid in ahydraulic line to a reserve tank such that negative pressure is created,and performs a negative pressure maintaining mode of maintaining thecreated negative pressure when creation of the negative pressure iscompleted. As the negative pressure creation mode and the negativepressure maintaining mode are executed, the piston in a caliperinstalled at each wheel may be withdrawn, and thus a drag phenomenon,which refers to incomplete separation between the brake and the disc,may be suppressed.

The braking control unit 50 is electrically connected to a wheel speedsensor 10, a pressure sensor 20, an accelerator pedal position sensor 30and a brake pedal position sensor 40. Thereby, the braking control unit50 may receive information about the vehicle including the wheel speed,pressure, accelerator pedal position, and brake pedal position measuredby the wheel speed sensor 10, the pressure sensor 20, the acceleratorpedal position sensor 30 and the brake pedal position sensor 40. Inaddition, the braking control unit 50 may receive the state informationabout the vehicle over a controller area network (CAN). Herein, thepressure sensor 20 is a sensor to measure the pressure of the fluidcoming out of the pressurizing cylinder.

Based on the state information about the vehicle received through theaforementioned various sensors, the braking control unit 50 determineswhether the vehicle is braking or traveling and performs a normalbraking mode upon determining that the vehicle is braking. In the normalbraking mode, the piston in the caliper is moved forward by thehydraulic pressure supplied from the master cylinder to cause the discand the brake pad to contact each other to produce friction,implementing the braking operation.

In the traveling situation, the braking control unit 50 executes anegative pressure creation mode to completely separate the disc from thebrake pads, and executes a negative pressure maintaining mode whencreation of the negative pressure is completed. When creation of thenegative pressure is completed, the braking control unit 50 performs thenegative pressure maintaining mode. However, when creation of thenegative pressure is not completed, the braking control unit 50 performsthe offset calibration of setting the position of the pressurizingpiston to the origin.

In addition, when operation in the normal mode is requested duringoperation in the negative pressure maintaining mode, the braking controlunit 50 stops the operation in the negative pressure maintaining mode,and performs the offset calibration of setting the last position of thepressurizing piston at atmospheric pressure to the origin. Thereby, whenoperation in the normal mode is requested during operation in thenegative pressure maintaining mode, the braking control unit 50 maystart the normal mode operation at the set position of the origin, whichis an atmospheric reference position.

In addition, when operation in the normal mode is requested duringoperation in the negative pressure creation mode, the braking controlunit 50 performs offset calibration of setting the current position ofthe pressurizing piston to the origin. Thereby, when operation in thenormal mode is requested during operation in the negative pressurecreation mode, the braking control unit 50 may start the normal modeoperation at the current set position of the pressurizing piston.

Whether or not creation of the negative pressure has been completed maybe determined based on the position of the pressurizing piston. That is,the braking control unit 50 determines that creation of the negativepressure has been completed when the pressurizing piston returns to aposition where it begins to perform an operation of securing space forcreation of the negative pressure. The position of the pressurizingpiston is calculated based on an angle of rotation measured by a Hallsensor in the motor connected to the pressurizing cylinder.

Referring to FIG. 2, the braking control unit 50 includes a receiver 51,a determination unit 52, a negative pressure creation unit 53, and anegative pressure maintaining unit 54.

The receiver 51 receives the state information about the vehicleincluding the brake pedal information, pedal pressure information,accelerator pedal information and wheel speed information which aremeasured by the sensors discussed above. In addition, the receiver 51may also receive the state information about the vehicle through aninterface (e.g., a CAN).

The determination unit 52 determines, based on the received stateinformation about the vehicle, whether the vehicle is braking ortraveling.

When the determination unit 52 determines that the vehicle is braking,the braking control unit 50 operates in the normal mode in which thepiston in the caliper is moved forward by the hydraulic pressuresupplied from the master cylinder to cause the disc and the brake padsto contact each other to implement braking.

When the determination unit 52 determines that the vehicle is traveling,the negative pressure creation unit 53 executes the negative pressurecreation mode. That is, in the negative pressure creation mode, theNormally-Open valve of each wheel is closed and the motor is driven tomove forward the pressurizing piston in the pressurizing cylinderconnected to the reserve tank in which the fluid is stored. Morespecifically, in the negative pressure creation mode, the fluid in thehydraulic line may be supplied to the reserve tank by the forwardmovement of the pressurizing piston, securing space for creation ofnegative pressure in the hydraulic line.

Referring to FIG. 4, the negative pressure creation unit 53 closes theNormally-Open valve 306 of each wheel FL, RR, RL, FR, and drives themotor 307, thereby moving the pressurizing piston of the pressurizingcylinder 303 forward. As the pressurizing piston of the pressurizingcylinder 303 is moved forward by driving the motor 307, the fluid issupplied back to the reserve tank RE.

The negative pressure maintaining unit 54 determines whether creation ofthe negative pressure has been completed by the negative pressurecreation unit 53. Upon determining that creation of the negativepressure has been completed, the negative pressure maintaining unit 54executes the negative pressure maintaining mode in which thepressurizing piston of the pressurizing cylinder 303 is withdrawn tomaintain the negative pressure.

When creation of the negative pressure by the negative pressure creationunit 53 is not completed, the negative pressure maintaining unit 54performs the offset calibration of setting the position of thepressurizing piston in the pressurizing cylinder to the origin. Inaddition, when the negative pressure maintaining unit 54 receives arequest for operation in the normal mode during execution of thenegative pressure maintaining mode, it stops the operation in thenegative pressure maintaining mode and performs the offset calibrationof setting the last position of the pressurizing piston at atmosphericpressure to the origin. Thereafter, the operation in the normal mode maybegin at an atmospheric pressure reference position, which is the setposition of the origin.

Referring to FIG. 5, the negative pressure maintaining unit 54 re-opensthe Normally-Open valve 306 of each wheel FL, RR, RL, FR, opens thevalve 302 connecting the wheels FL, RR, RL and FR to the pressurizingcylinder 303, closes a valve 301 connecting the reserve tank RE to thewheel cylinders, closes a valve 304 connecting the reserve tank RE tothe pressurizing cylinder 303, and drives the motor 307 to withdraw thepressurizing piston in the pressurizing cylinder 303 until the pistonreaches a flow passage 305 connecting the reserve tank RE to thepressurizing cylinder 303. As the negative pressure in the hydraulicline is maintained in this way, the brake pads may be completelyseparated from the disc, and accordingly drag may be reduced.

Hereinafter, a method of controlling the brake system having a dragreduction function configured as above will be described with referenceto FIG. 3.

FIG. 3 is a flowchart illustrating a method of controlling a brakesystem having a drag reduction function according to one embodiment ofthe present invention.

Referring to FIG. 3, the braking control unit 50 receives the stateinformation of the vehicle (S11). That is, the braking control unit 50receives the measured information from the wheel speed sensor 10, thepressure sensor 20, the accelerator pedal position sensor 30 and thebrake pedal position sensor 40.

The braking control unit 50 determines whether the vehicle is braking ortraveling, using the received state information about the vehicle (S13).

Upon determining in operation S13 that the vehicle is braking, namely,that a brake pedal manipulation signal or pedal pressure information, orboth are received, the braking control unit 50 executes the normal mode(S14). In the normal mode, hydraulic pressure is supplied from themaster cylinder, and thus the piston in the caliper moves forward,causing the brake pads and the disc to contact each other to performbraking.

Upon determining in operation S13 that the vehicle is not braking, thebraking control unit 50 determines whether the vehicle is traveling(S15).

Upon determining in operation S15 that the vehicle is not traveling, thebraking control unit 50 moves to operation S14 in the process, andexecutes the normal mode.

Upon determining in operation S15 that the vehicle is traveling, thebraking control unit 50 executes the negative pressure creation mode(S17). As described above, in the negative pressure creation mode, theNormally-Open valve 306 of each wheel is closed, and the motor 307 isdriven to move the pressurizing piston in the pressurizing cylinder 303such that the fluid in the hydraulic line is supplied to the reservetank RE. Thereby, negative pressure is created.

Thereafter, the braking control unit 50 determines whether creation ofthe negative pressure has been completed. (S19). At this time, thebraking control unit 50 may determine, based on the position of thepressurizing piston in the pressurizing cylinder 303, whether creationof the negative pressure has been completed. The position of thepressurizing piston is calculated based on an angle of rotation measuredby a Hall sensor in the motor 307. That is, the braking control unit 50determines that creation of the negative pressure has been completedwhen the pressurizing piston returns to a position where it begins toperform an operation of securing space for creation of the negativepressure.

Upon determining in operation S19 that creation of the negative pressureis not completed, the braking control unit 50 performs offsetcalibration of forcing the pressurizing piston in the pressurizingcylinder 303 to return to the origin (S20).

Upon determining in operation S19 that creation of negative pressure hasbeen completed, the braking control unit 50 executes the negativepressure maintaining mode (S21). As described above, in the negativepressure maintaining mode, the Normally-Open valve 306 of each wheel FL,RR, RL, FR is re-opened, the valve 302 connecting the wheels FL, RR, RLand FR to the pressurizing cylinder 303 is opened, a valve 301connecting the reserve tank RE to the wheel cylinders is closed, a valve304 connecting the reserve tank RE to the pressurizing cylinder 303 isclosed, and the motor 307 is driven to withdraw the pressurizing pistonin the pressurizing cylinder 303 until the piston reaches a flow passage305 connecting the reserve tank RE to the pressurizing cylinder 303.Thereby, the negative pressure is maintained in the section from thevalve 301, which connects the reserve tank RE to the wheel cylinders, tothe wheel cylinders, and accordingly the piston in the caliper iswithdrawn. Thereby, the brake pads and the disc are kept spaced apartfrom each other, and therefore drag between the brake pads and the discmay be reduced.

As is apparent from the above description, according to one embodimentof the present invention, negative pressure is created by controllingthe position of a pressurizing piston in a pressurizing cylinderconnected to a reserve tank through a motor such that a fluid in ahydraulic line is supplied to the reserve tank. Accordingly, the pistonin a caliper may be forcibly withdrawn, more effectively reducing drag.

In addition, according to one embodiment, when operation in a normalmode is requested during execution of a negative pressure creation mode,the negative pressure creation mode is interrupted, and an offsetcalibration of setting the position of the pressurizing piston to theorigin is performed. When operation in a normal mode is requested duringexecution of a negative pressure maintaining mode, offset calibration ofsetting the last position of the pressurizing piston at atmosphericpressure to the origin is performed. Thereby, loss of brakeresponsiveness and brake feel may be minimized.

Although a few embodiments of the present invention have been shown anddescribed, it would be appreciated by those skilled in the art thatchanges may be made to the embodiments without departing from theprinciples and spirit of the invention, the scope of which is defined inthe claims and their equivalents.

What is claimed is:
 1. A brake system to perform braking to decelerateor stop a vehicle, the brake system comprising: a pressurizing cylinderconnected to a reserve tank adapted to store a fluid; a motor to move apressurizing piston forward in the pressurizing cylinder; and a brakingcontrol unit to receive state information about the vehicle to determinewhether the vehicle is braking or traveling, execute, when the vehicleis traveling, a negative pressure creation mode of driving the motor tomove the pressurizing piston forward to create a negative pressure, andexecute, when creation of the negative pressure is completed, a negativepressure maintaining mode of maintaining the negative pressure.
 2. Thebrake system according to claim 1, wherein, in the negative pressurecreation mode, a Normally-Open valve of each wheel is closed, and themotor is driven to move the pressurizing piston forward such that afluid in a hydraulic line is supplied to the reserve tank.
 3. The brakesystem according to claim 1, wherein, in the negative pressuremaintaining mode, a Normally-Open valve of each wheel is re-opened, avalve connecting the wheel to the pressurizing cylinder is opened, avalve connecting the reserve tank to a wheel cylinder is closed, a valveconnecting the reserve tank to the pressurizing cylinder is closed, andthe pressurizing piston is withdrawn in the pressurizing cylinder untilthe pressurizing piston reaches a flow passage connecting the reservetank to the pressurizing cylinder, such that the negative pressure ismaintained.
 4. The brake system according to claim 1, wherein the stateinformation about the vehicle comprises information items measuredrespectively by a wheel speed sensor, a pressure sensor, an acceleratorpedal position sensor and a brake pedal position sensor, wherein thebraking control unit determines whether the vehicle is braking based onbrake pedal manipulation information and pedal pressure information ofthe state information about the vehicle, and determines whether thevehicle is traveling based on accelerator pedal information and wheelspeed information of the state information about the vehicle.
 5. Thebrake system according to claim 1, wherein the braking control unitdetermines whether the creation of the negative pressure has beencompleted after executing the negative pressure creation mode, andperforms, when the creation of the negative pressure has not beencompleted, or execution of the negative pressure maintaining mode isinterrupted, offset calibration of calibrating a position of thepressurizing piston.
 6. The brake system according to claim 5, whereinthe braking control unit performs, when the execution of the negativepressure creation mode is interrupted or the creation of the negativepressure has not been completed, offset calibration of setting theposition of the pressurizing piston to an origin, and performs, when theexecution of the negative pressure maintaining mode is interrupted,offset calibration of setting a last position of the pressurizing pistonat an atmospheric pressure to an origin.
 7. A method of controlling abrake system including a pressurizing cylinder connected to a reservetank adapted to store a fluid and a motor to move a pressurizing pistonforward in the pressurizing cylinder, the method comprising: receivingstate information about a vehicle; determining whether the vehicle isbraking or traveling based on the received state information; executing,when it is determined, in the determining, that the vehicle istraveling, a negative pressure creation mode of driving the motor tomove the pressurizing piston forward to create a negative pressure, andexecuting, when creation of the negative pressure is completed, anegative pressure maintaining mode of maintaining the negative pressure.8. The method according to claim 7, wherein the executing of thenegative pressure creation mode comprises closing a Normally-Open valveof each wheel, and driving the motor to move the pressurizing pistonforward such that a fluid in a hydraulic line is supplied to the reservetank.
 9. The method according to claim 7, wherein the executing of thenegative pressure maintaining mode comprises re-opening a Normally-Openvalve of each wheel, opening a valve connecting the wheel to thepressurizing cylinder, closing a valve connecting the reserve tank to awheel cylinder, closing a valve connecting the reserve tank to thepressurizing cylinder, and withdrawing the pressurizing piston in thepressurizing cylinder until the pressurizing piston reaches a flowpassage connecting the reserve tank to the pressurizing cylinder, suchthat the negative pressure is maintained.
 10. The method according toclaim 7, wherein the executing comprises: determining, after executingthe negative pressure creation mode, whether the creation of thenegative pressure has been completed; and performing, when it isdetermined in the determining that the creation of the negative pressurehas not been completed, offset calibration of calibrating a position ofthe pressurizing piston.
 11. The method according to claim 10, whereinthe performing of the offset calibration comprises: performing, when theexecution of the negative pressure creation mode is interrupted, offsetcalibration of setting the position of the pressurizing piston to anorigin, and performing, when the execution of the negative pressuremaintaining mode is interrupted, offset calibration of setting a lastposition of the pressurizing piston at an atmospheric pressure to anorigin.